Semiconductor Package and Method of Forming the Same

ABSTRACT

A method of forming a semiconductor package includes receiving a carrier, coating the carrier with a bonding layer, forming a first insulator layer over the bonding layer, forming a backside redistribution layer over the first insulator layer, forming a second insulator layer over the backside redistribution layer, patterning the second insulator layer to form a recess that extends through the second insulator layer and to the backside redistribution layer, filling the recess with a solder, and coupling a surface-mount device (SMD) to the solder.

CROSS-REFERENCE TO A RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No. 14/470,999, filed Aug. 28, 2014, which is incorporated herein by reference in its entirety.

BACKGROUND

For mobile applications, a form factor refers to a mobile device's size, shape, and style, as well as the layout and position of the components. Consumers prefer devices with a thinner form factor, making manufacture of the device more difficult. Therefore, there is a need to meet the above demand.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a sectional view illustrating an exemplary semiconductor package in accordance with some embodiments.

FIGS. 2-10 are sectional views illustrating the exemplary semiconductor package in accordance with some embodiments.

FIG. 10 is a sectional view illustrating an exemplary semiconductor package in accordance with some embodiments.

FIGS. 11-19 are sectional views illustrating the exemplary semiconductor package in accordance with some embodiments.

FIGS. 20(a), 20(b) are top views illustrating the shape of the pad in the backside redistribution layer of the exemplary semiconductor package and its contact with the SMD component by using solders in accordance with some embodiments.

FIGS. 21(a), 21(b) are top views illustrating the shape of the pad in the backside redistribution layer of the exemplary semiconductor package and its contact with the SMD component by using solders in accordance with some embodiments.

FIGS. 22(a), 22(b) are top views illustrating the shape of the pad in the backside redistribution layer of the exemplary semiconductor package and its contact with the SMD component by using solders in accordance with some embodiments.

FIGS. 23, 24 are top views illustrating the shape of the pad in the backside redistribution layer of the exemplary semiconductor package in accordance with some embodiments.

FIG. 25 is a flow chart for a method of forming a semiconductor package comprising a chip and a component in accordance with some embodiments.

FIG. 26 is a flow chart for a method of forming a semiconductor package comprising a chip and a component in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

For mobile application, a form factor refers to a mobile device's size, shape, and style, as well as the layout and position of the components, such as embedded SMD components and chips. Consumers prefer devices with a thinner form factor, which makes manufacture of the devices more difficult.

In order to reach the thinner package form factor without sacrificing signal integrity, the SMD components may be placed between the substrate (e.g., PCB) and the chips, and by the side of ball grid array (“BGA”) balls. The distance therebetween is determined by the BGA balls. The SMD components should have a height which is less than a stand-off height of the BGA balls. In one embodiment, the height of the SMD components is about 130-150 micrometers; the height of the pre-solder is about 20 micrometers; and the stand-off-height of the BGA balls is about 140-170 micrometers. It has been demonstrated that the design margin for the placement of the SMD components is very tight. Therefore, to enlarge the design margin, this disclosure embeds the SMD in the molding.

In one embodiment, a new package structure is disclosed. Some pads of a backside redistribution layer (B/S RDL) in the package are designed with an open structure. By using the open structure, the molding material can flow into the space under the SMD component.

The chip may be selected from the group consisting of silicon semiconductors or III-V semiconductors. The chips may include a microelectromechanical system (MEMS).

FIG. 1 is a sectional view illustrating an exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 1, a temporary bonding layer 104 is coated over a carrier 102. The carrier 102 may be formed of, for example, metal or glass. The temporary bonding layer 104 is formed of, for example, glue.

An insulator layer 106 is formed over the temporary bonding layer 104. The insulator layer 106 may be formed of, for example, epoxy or polymer. A backside redistribution layer 108 is formed over the insulator layer 106, then, the backside redistribution layer 108 is patterned by using a mask (not shown). The material for the backside redistribution layer 108 may include, but is not limited to, for example, Cu, Al, AlCu, Al alloy, Cu alloy, or other conductive materials.

FIG. 2 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 2, a pre-solder (not shown) is provided over a portion 202 of the backside redistribution layer 108. An SMD component 204 is provided over the backside redistribution layer 108. The pre-solder (not shown) is disposed between the SMD component 204 and the portion 202 of the backside redistribution layer 108. The SMD component 204 may be, for example, passive components, such as resistor, inductors, or capacitors.

FIG. 3 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 3, a chip 302 is provided over the backside redistribution layer 108. In details, the chip 302 adheres to the backside redistribution layer 108 by a glue layer 310. The chip 302 includes a die 303, an interconnect layer 304, a passivation layer 305, and a sacrificial layer 306. The interconnect layer 304 includes interconnections 314. The passivation layer 305 includes a pad 315. The sacrificial layer 306 includes a copper (Cu) pillar 316. The die 303 connects to the Cu pillar 316 through the interconnections 314 and the pad 315. The interconnect layer 304 may be made of low-k material. The sacrificial layer 306 may be made of polymer. In the embodiments, the chip 302 may be selected from the group consisting of silicon semiconductors or III-V semiconductors. The chips may include a microelectromechanical system (MEMS). FIG. 4 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 4, a molding compound 402 is provided over the SMD component 204 and adjacent to the chip 302. The molding compound 402 may be made of silica, organic materials, or epoxy resins. The molding step may be performed to form the molding compound 402 surrounding the SMD component 204 and adjacent to the chip 302. The molding compound 402 may be partially removed from the top of the chip 302 to expose the upper surface of the chip 302.

FIG. 5 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 5, a via hole 502 is opened in the molding compound 402. In the embodiment, the via hole 502 exposes the backside redistribution layer 108.

FIG. 6 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 6, a via 602 is provided in the via hole 502 of the molding compound 402, and the via 602 electrically connects to the backside redistribution layer 108. The via 602 may be made of, for example, copper or tin. In the embodiment, the formation of the molding compound 402 and the via 602 includes: first forming the molding compound 402; opening the via hole 502 in the molding compound 402 to expose the backside redistribution layer 108; and then forming the via 602 in the via hole 502. In some embodiments, such formation may include: first forming the via 602; and then forming the molding compound 402. That is, the sequence of the formation of the molding compound 402 and the via 602 may alter.

FIG. 7 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 7, the portion 202 and the portion of 704 of the backside redistribution layer 108 are connected, then a front redistribution layer 702 is provided over the chip 302 and the via 602 to connect the chip 302 and the SMD component 204 by using the backside redistribution layer 108, the via 602, and the front redistribution layer 702. The front redistribution layer 702 surrounded by a polybenzoxazole (PBO) layer 706 may include a trace 711 and an under bump metal (UBM) 712. The end of the trace 711 may provide a landing pad (not shown).

The trace 711 and the PBO layer 706 can be either a single layer or stacked multiple layers. In the embodiment with the trace 711 and the PBO layer 706 having stacked multiple layers, the formation of the PBO layer 706 and the trace 711 may include: forming a first PBO layer over the chip 302 and the molding compound 402; etching the first PBO layer and forming a first trace layer in the etched portion; repeating the formation and the etching process; and forming the UBM 712 over the end of the trace 711 (landing pad). The material for the front redistribution layer 702 may comprise, but is not limited to, for example Cu, Al, AlCu, Al alloy, Cu alloy, or other conductive materials. As such, a semiconductor package 700 is provided. The SMD components 204 are placed in the molding compound 402 and are not placed between BGA balls. So the SMD components 204 are no longer constrained by a height which is less than the stand-off-height of the BGA balls. While having a thinner package form factor without sacrificing signal integrity, the design margin for placement of the SMD components 204 relaxes.

FIG. 8 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 8, a plurality of metal bumps 802 are provided and connected to the chip 302 and the SMD component 204 by the front redistribution layer 702. The formation of the metal bumps 802 on the front redistribution layer 702 may be realized by, for example, ball grid array (BGA) solder bumping, which is a type of surface-mount packaging. FIG. 9 is a sectional view illustrating the exemplary semiconductor device using the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 9, the semiconductor package 700 is debonded from the carrier 102. The insulator layer 106 and the temporary bonding layer 104 of the semiconductor package 700 are opened. The semiconductor package 700 is flipped upside down and connected to a printed circuit board 914.

In the embodiment, the semiconductor package 902 includes two stacked mobile DDRs (or LPDDR) 904, 905 and a packaging substrate 903. The packaging substrate 903 includes a redistribution layer (not shown) similar to the abovementioned, and connects to the two mobile DDRs 904, 905 through bonding wires 906. Metal bumps 910 provide electrical connection between the backside redistribution layer 108 and the packaging substrate 903. Therefore, the semiconductor package 902 is bonded to the backside redistribution layer of the semiconductor packages 700, so that a package-on-package structure 900 including the semiconductor packages 700, 902 is provided.

FIG. 10 is a sectional view illustrating an exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 10, a temporary bonding layer 1004 is coated over a carrier 1002. The carrier 1002 may be formed of, for example, metal or glass. The temporary bonding layer 1004 is formed of, for example, glue.

A first insulator layer 1006 is formed over the temporary bonding layer 1004. The first insulator layer 1006 may be formed of, for example, epoxy or polymer. A backside redistribution layer 1008 is formed over the first insulator layer 1006, then, the backside redistribution layer 1008 is patterned by using a mask (not shown). The material for the backside redistribution layer 1008 may comprise, but is not limited to, for example Cu, Al, AlCu, Al alloy, Cu alloy, or other conductive materials.

FIG. 11 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 11, a second insulator layer 1102 is formed over the backside redistribution layer 1008 and the first insulator layer 1006. Then the second insulator layer 1102 is patterned to form a recess 1106 exposing a portion of the backside redistribution layer 1008. The second insulator layer 1102 may be formed of, for example, epoxy or polymer. A detail portion 1104 for solder wetting will be described.

FIG. 12 is a sectional view illustrating detail portion 1104 of the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 12, a pre-solder 1202 is provided in the recess 1106 of the second insulator layer 1102. Another pre-solder 1203 is attached to the SMD component 1204.

FIG. 13 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 13, the pre-solders 1202, 1203 are combined to produce a solder joint and disposed between the SMD component 1204 and the portion 1206 of the backside redistribution layer 1008, so the SMD component 1204 contacts with the pre-solders 1202, 1203 in the recess of the second insulator layer 1102. The SMD component 1204 may be passive components, such as resistor, inductors or capacitors.

FIG. 14 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 14, a chip 1402 is provided over the second insulator layer 1102. The chip 1402 may be selected from the group consisting of silicon semiconductors or III-V semiconductors. The chips may include a microelectromechanical system (MEMS).

FIG. 15 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 15, a molding compound 1502 is provided over the SMD component 1204 and adjacent to the chip 1402. The molding compound 1502 may be made of silica, organic materials, or epoxy resins. The molding step may be performed to form the molding compound 1502 surrounding the SMD component 1204 and adjacent to the chip 1402. The molding compound 1502 may be partially removed from the top of the chip 1402 to expose the upper surface of the chip 1402.

Before providing the molding compound 1502, a portion of the second insulator layer 1102 is removed to form a recess and to expose a portion 1506 of the backside redistribution layer 1008, and a conductive material 1504 is filled in the recess for further electrical connection.

FIG. 16 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 16, a via hole 1602 is opened in the molding compound 1502.

FIG. 17 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 17, a via 1702 is provided in the via hole 1602 of the molding compound 1502.

FIG. 18 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 18, the portion 1206 and the portion of 1506 of the backside redistribution layer 1108 are connected, then a front redistribution layer 1802 is provided over the chip 1402 and the via 1702 to connect the chip 1402 and the SMD component 1204 by using the backside redistribution layer 1108, the via 1702, and the front redistribution layer 1802. The material for the front redistribution layer 1802 may comprise, but is not limited to, for example Cu, Al, AlCu, Al alloy, Cu alloy, or other conductive materials. As such, a semiconductor package 1800 is provided.

The SMD components 1204 are placed in the molding compound 1502 and are not placed between BGA balls. So the SMD components 1204 are no longer constrained by a height which is less than the stand-off-height of the BGA balls. While having a thinner package form factor without sacrificing signal integrity, the design margin for placement of the SMD components 1204 relaxes.

FIG. 19 is a sectional view illustrating the exemplary semiconductor package in accordance with some embodiments. As shown in FIG. 19, a plurality of metal bumps 1902 are provided and connected to the chip 1402 and the SMD component 1204 by the front redistribution layer 1802. Furthermore, the semiconductor package 1800 is debonded from the carrier 1002. The semiconductor package 1800 may be provided over and connected to a printed circuit board (not shown).

In the embodiment, the sequence of the processes abovementioned provides an example and does not limit scope of the disclosure. There are other possibilities to realize the semiconductor package and the method of forming the same, such as an alternative sequence which fabricates the via 1702 prior to the molding compound 1502.

FIGS. 20(a), 20(b) are top views illustrating the shape of the pad in the backside redistribution layer of the exemplary semiconductor package and its contact with the SMD component by using solders in accordance with some embodiments. As shown in FIG. 20(a), a pad 2002 with a notch 2003 is provided in the backside redistribution layer. The notch 2003 is designed to define location of the pad 2002. The width of the pad 2002 is about 450 micrometers; the length of the pad 2002 is about 400 micrometers. The width and the length of the notch 2003 are about 2-10 micrometers. As shown in FIG. 20(b), a pre-solder 2006 is placed over the pad 2002 for joining the pad 2002 and an SMD component 2004. The pre-solder 2006 is confined by the notch 2003.

FIGS. 21(a), 21(b) are top views illustrating the shape of the pad in the backside redistribution layer of the exemplary semiconductor package and its contact with the SMD component by using solders in accordance with some embodiments. As shown in FIG. 21(a), a pad 2102 with a slot 2103 is provided in the backside redistribution layer. The slot 2103 is designed to define location of the pad 2102. The width of the pad 2102 is about 450 micrometers; the length of the pad 2102 is about 400 micrometers. The width of the slot 2103 is about 30-60 micrometers; the length of the slot 2103 is about 20 micrometers. The number of the slots is not limited and varies based on pad designs. As shown in FIG. 21(b), a pre-solder 2106 is placed over the pad 2102 for joining the pad 2102 and an SMD component 2104. The pre-solder 2106 is confined by the slot 2103. Additionally, different shapes of the slots can be applied for stopping solder wetting expansion.

FIGS. 22(a), 22(b) are top views illustrating the shape of the pad in the backside redistribution layer of the exemplary semiconductor package and its contact with the SMD component by using solders in accordance with some embodiments. As shown in FIG. 22(a), a u-shape pad 2202 with a open structure 2203 is provided in the backside redistribution layer. The open structure 2203 is designed to define location of the u-shape pad 2202. The width of the open structure 2203 is about 450 micrometers; the length of the open structure 2203 is about 50 micrometers. As shown in FIG. 22(b), a pre-solder 2206 is placed over the u-shape pad 2202 to join the u-shape pad 2202 and an SMD component 2204. By using the open structure 2203, the molding material can flow into the space under the SMD component 2204.

FIGS. 23, 24 are top views illustrating the shape of the pad in the backside redistribution layer of the exemplary semiconductor package in accordance with some embodiments. In order to stop solder wetting expand, different shapes and combinations of the slots can be applied, such as a pad 2302 having three aligned slots in FIG. 23, and even a pad 2402 having four slots in FIG. 24.

FIG. 25 is a flow chart for a method of forming a semiconductor package comprising a chip and a component in accordance with some embodiments. As shown in FIG. 25, a method 2500 is provided. The method 2500 includes the following operations: providing a temporary bonding layer over a carrier (2502); forming an insulator layer over the temporary bonding layer (2504); forming a backside redistribution layer over the insulator layer (2506); providing a pre-solder over a portion of the backside redistribution layer (2508); providing the chip and the component over the backside redistribution layer and contacting the component to the pre-solder (2510).

The operation 2506 further includes forming a pad having a notch in the backside redistribution layer. The operation 2506 further includes forming a pad having a slot in the backside redistribution layer. The operation 2506 further includes forming a u-shape pad having a open structure in the backside redistribution layer. The method 2500 further includes providing a plurality of metal bumps connected to the chip and the component by the front redistribution layer. The method 2500 further includes: providing a molding compound over the component and adjacent to the chip; opening a via hole in the molding compound; providing a via in the via hole of the molding compound; and providing a front redistribution layer over the chip and the via to connect the chip and the component by using the backside redistribution layer, the via and the front redistribution layer; debonding the semiconductor package from the carrier; and providing the semiconductor package over and connected to a printed circuit board. The operation 2510 further includes providing a surface-mount device (SMD) over the backside redistribution layer. The operation 2504 further includes forming the insulator layer made of polymer over the temporary bonding.

FIG. 26 is a flow chart for a method of forming a semiconductor package comprising a chip and a component in accordance with some embodiments. As shown in FIG. 26, a method 2600 is provided. The method 2600 includes the following operations: providing a temporary bonding layer over a carrier (2602); forming a first insulator layer over the temporary bonding (2604); forming a backside redistribution layer over the insulator layer (2606); forming a second insulator layer over the backside redistribution layer (2608); patterning the second insulator layer to form a recess exposing a portion of the backside redistribution layer (2610); providing a pre-solder in the recess of the second insulator layer (2612); providing the chip and the component over the second insulator layer, and contacting the component to the pre-solder in the recess of the second insulator layer (2614).

The operation 2606 further includes forming a pad having a notch in the backside redistribution layer. The operation 2606 further includes forming a pad having a slot in the backside redistribution layer. The operation 2606 further includes forming a u-shape pad having a open structure in the backside redistribution layer. The method 2600 further includes providing a plurality of metal bumps connected to the chip and the component by the front redistribution layer. The method 2600 further includes: providing a molding compound over the component and adjacent to the chip; opening a via hole in the molding compound and the second insulator layer; providing a via in the via hole of the molding compound and the second insulator layer; and providing a front redistribution layer over the chip and the via to connect the chip and the component by using the backside redistribution layer, the via and the front redistribution layer; debonding the semiconductor package from the carrier; and providing the semiconductor package over and connected to a printed circuit board. The operation 2614 further includes providing a surface-mount device (SMD) over the second insulator layer.

According to an exemplary embodiment, a method of forming a semiconductor package comprises: receiving a carrier; coating the carrier with a bonding layer; forming a first insulator layer over the bonding layer; forming a backside redistribution layer over the first insulator layer; forming a second insulator layer over the backside redistribution layer; patterning the second insulator layer to form a recess that extends through the second insulator layer and to the backside redistribution layer; filling the recess with a solder; and coupling a surface-mount device (SMD) to the solder.

According to an exemplary embodiment, a semiconductor package comprises: a first insulator layer; a backside redistribution layer over the first insulator layer; a second insulator layer over the backside redistribution layer; a surface-mount device (SMD) over the second insulator layer; and a solder extending through the second insulator layer and coupled to the backside redistribution layer and the SMD.

According to an exemplary embodiment, a semiconductor package comprises a backside redistribution layer, a surface-mount device (SMD), a pad between the backside redistribution layer and the SMD, and a solder joining the backside redistribution layer, the SMD, and the pad.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of forming a semiconductor package, the method comprising: receiving a carrier; coating the carrier with a bonding layer; forming a first insulator layer over the bonding layer; forming a backside redistribution layer over the first insulator layer; forming a second insulator layer over the backside redistribution layer; patterning the second insulator layer to form a recess that extends through the second insulator layer and to the backside redistribution layer; filling the recess with a solder; and coupling a surface-mount device (SMD) to the solder.
 2. The method of claim 1, further comprising providing a molding compound over the SMD.
 3. The method of claim 2, further comprising providing a chip adjacent the molding compound, wherein providing the molding compound includes providing the molding compound over the chip, and removing the molding compound on a top surface of the chip.
 4. The method of claim 3, further comprising forming a front redistribution layer coupled to the top surface of the chip.
 5. The method of claim 4, further comprising: forming a via hole that extends through the molding compound and the second insulator layer and to the backside redistribution layer; and filling the via hole with a via material, wherein forming the front redistribution layer includes forming the front redistribution layer coupled to the via material.
 6. The method of claim 4, further comprising providing a plurality of metal bumps coupled to the front redistribution layer.
 7. The method of claim 1, further comprising: debonding the carrier from the semiconductor package; and providing a plurality of metal bumps extending through the first insulator layer and coupled to the backside redistribution layer.
 8. A semiconductor package comprising: a first insulator layer; a backside redistribution layer over the first insulator layer; a second insulator layer over the backside redistribution layer; a surface-mount device (SMD) over the second insulator layer; and a solder extending through the second insulator layer and coupled to the backside redistribution layer and the SMD.
 9. The semiconductor package of claim 8, further comprising a molding compound over the SMD.
 10. The semiconductor package of claim 9, further comprising a chip adjacent the molding compound and having a top surface, wherein the molding compound has a top surface flush with the top surface of the chip.
 11. The semiconductor package of claim 10, further comprising a front redistribution layer coupled to the top surface of the chip.
 12. The semiconductor package of claim 11, further comprising a via extending through the molding compound and the second insulator layer and coupled to the backside redistribution layer and the front redistribution layer.
 13. The semiconductor package of claim 11, further comprising a metal bump coupled to one of the backside redistribution layer and the front redistribution layer.
 14. A semiconductor package comprising: a backside redistribution layer; a surface-mount device (SMD); a pad between the backside redistribution layer and the SMD; and a solder joining the backside redistribution layer, the SMD, and the pad.
 15. The semiconductor package of claim 14, further comprising: a molding compound over the SMD and having a top surface; and a chip adjacent the molding compound and having a top surface substantially flush with the top surface of the molding compound.
 16. The semiconductor package of claim 15, further comprising: a front redistribution layer coupled to the top surface of the chip; and a via extending through the molding compound and coupled to the backside redistribution layer and the front redistribution layer.
 17. The semiconductor package of claim 16, further comprising a metal bump coupled to one of the backside redistribution layer and the front redistribution layer
 18. The semiconductor package of claim 14, wherein the pad has an edge and is formed with a notch at the edge thereof and the solder is confined by the notch.
 19. The semiconductor package of claim 14, wherein the pad is formed with slot therethrough and the solder is confined by the slot.
 20. The semiconductor package of claim 14, wherein the pad is u-shape. 